1. Invention
The field of the present invention relates, in general, to seat assemblies of the type commonly found in office and living environments, and more particularly, to seat assemblies having adjustable mechanisms with movable seats and movable backrests and methods for supporting the occupant thereon.
Further, it relates to seat assemblies that add the self-adjusting dynamic mechanisms to follow the users movements and balancing the weight with the supporting counter balanced action of the mechanism during use.
2. Description of Related Art
Considerable work has been directed toward the development of seat assemblies or chairs which are ergonomically well suited for use by persons who are engaged in tasks that require that they be seated for prolonged periods of time. Typical of such applications are the seats or chairs which are used in offices or at home for tasks such as typing, reading and computer use.
In recent years it has been recognized that it is highly desirable for such seat assemblies or chairs to be constructed in a manner which allows the seat to move along an upwardly concaved arcuate path, or some approximation thereof. Such arcuate movement is most desirably implemented by mounting the seat for movement about an arcuate path having a center of curvature which is proximate the center of mass of the person seated on the seat. This geometry dynamically balances the bio-mechanics of user's body with movement of the chair so that the user can have a plurality of equilibrium positions in a variety of postures. The design principle is one of counterbalanced motion in which the mass of the user's body is counterbalanced by angular forces of the motion of the seat mechanism in primarily a fore-and-aft direction.
People are accustomed to conventional static seat technology and the subjective perception that it is stable. Seating advancements to date deal with ergonomic concerns, cushion contouring, and tilt adjustments that typically are unstable unless locked in place. Such chairs are not responsive to the body's motion. For example, the low back and thighs lose support when the buttock slides forward on the seat by any small amount. This makes the seat unsafe as well as uncomfortable.
My previous U.S. Pat. Nos. 5,244,252; 5,460,427; 5,558,399, and 5,735,574, describe in more detail the advantages of mounting a seat for movement along an upwardly concaved path having a center of curvature proximate the center of mass of the person seated on the seat. These patents are incorporated herein by reference. Such seat assemblies also are particularly well suited for use in vehicles to dissipate the dynamic forces generated when the vehicle is involved in a sudden deceleration or crash.
In addition to mounting the seat of a chair for arcuate movement, it is also well known to mount the back of the seat assembly for movement or for movement of a portion of the back, such as the lumbar support region. Various schemes for moving the back are also disclosed in my above-referenced patents. Most of these movable back mounting systems couple the back to the seat and have been designed primarily for dynamic deceleration of the seat assembly in vehicles, but they are usable to varying degrees in office or home seating.
U.S. Pat. Nos. 5,261,732; 5,366,269; 5,437,494; 5,577,802; 5,961,073; 5,979,984, 6,334,648, and 7,234,775 disclose chairs or seat assemblies in which one or both of the back and seat are mounted for movement. It is important to note that differences in the manners in which the seats and/or seat backs are mounted for movement make the dynamic performance of these assemblies vastly different, even though there are superficial similarities. It is not enough to observe that movable seat and/or seat backs are known in the prior art.
By way of example, U.S. Pat. No. 5,261,732 to Hosoe, includes both a movable seat and movable seat back. It is clear, however, that the seat back in the Hosoe patent seat can move along an arcuate path, but the seat back in the Hosoe can only move vertically. There is a lever coupled between the seat and seat base in Hosoe which constrains motion seat back. The lever in Hosoe synchronizes seat motion with the height adjustment mechanism and thereby stops independent, free rotation of the user's pelvis by stopping the seat when the height is set.
In the present invention, unlike prior art such as Hosoe, the seat and the seat back are mounted for independent motion so that many, many independent equilibrium positions can be achieved for support in various seating postures and during the change between said postures.
It is, of course, also well known in office chairs to provide for backrest reclining mechanisms as, for example, are shown in U.S. Pat. Nos. 5,975,634 and 6,086,153. Seat and Backrest adjustments designed to be locked during use alone are not the same as a seat and a seat back which are mounted for independent movement during use.
Generally, therefore, there still remains a need for a chair or seating assembly which can be used for long periods of time that has an independently movably seat and an independently movable backrest which will together accommodate a wide range of seating postures while providing many balanced or equilibrium positions matched to the bio-mechanics of the user's body. Thus, the person using the chair will want to assume various postures, such as a forward reaching posture (where the person is performing manual tasks on a support surface such as a desk), or an erect posture (for tasks such as typing), or a semi-reclined posture for increased relaxation. The seat and backrest should be independently movable to an equilibrium position about which dynamic micro-adjustments of the user's body and the seat assembly about the center of mass of the user are possible in order to provide the greatest comfort during prolonged use.
A similar example of a chair assembly which has both a movable seat and a movable backrest is disclosed in U.S. Pat. No. 6,523,898 to Ball et al. In the Ball et al. patent, the seat assembly is mounted for arcuate movement along a path having a center of rotation below, not above, the seat. Thus, the seat moves about a combination of pivot points, which are below the seat, and the resulting path of seat motion is downwardly concaved. This can be very clearly seen in Ball et al. by comparing numeral 53 in FIG. 5 with numeral 53 in FIG. 7. The front of the seat in Ball et al. dives or rotates downwardly about a center of rotation which is below the seat and proximate the center post. The desired upwardly concaved arcuate path, which has been found to be desirable to achieving equilibrium of motion for many seat postures, is not present, therefore, in Ball et al. Instead, a seat motion which rotates the seat downwardly is present.